(Important Facts)
Alcohol fermentation of sugars by enzymes has long been known as a method for producing alcohols.
Alcohol fuels have recently attracted much attention because of situation with energy, and the E3 project in which 3% ethanol is mixed with gasoline has been started in Japan. Appeals to wean ourselves from dependence on fossil fuels have been heard for a long time.
In order to replace petroleum with ethanol, it is necessary to guarantee the availability of large amounts of sugar (glucose, fructose, cane sugar, and the like) as raw material. However, even in the case of sugar cane, the yield of sugar from stems is 10 to 20%, major part of stems and leaves is comprised of lignocellulose, which is difficult to decompose, and it is difficult to produce alcohol therefrom by an enzyme within a short time without other modification.
(Conventional Technology)
Methods for producing glucose and for producing ethanol by decomposing lignocellulose on an industrial scale have recently attracted attention. Typical methods of this type are disclosed in JP-A-61-261358, JP-A-62-79230, JP-A-2-101093, JP-A-5-140322, JP-A-5-140323, JP-A-6-12277, JP-A-6-226711, JP-A-7-118293, JP-A-8-157666, JP-A-8-225653, JP-A-8-260231, JP-A-8-299000, JP-A-10-66594, JP-A-10-110001, JP-A-10-251522, JP-A-11-36191, JP-A-11-325921, JP-A-2002-85100, JP-A-2003-213584, JP-A-2003-342289, JP-A-2005-168335, JP-A-2005-239979, JP-A-2005-40106, JP-A-2005-263527, JP-A-2006-75007, JP-A-2006-281037, International Patent Application Publication WO00-53832, and the like.
Basically, methods of three groups are used: (a) a process of producing ethanol from starch and saccharic starting materials; (b) a process of producing ethanol by hydrolyzing a cellulose-based source material with an acid or the like (including a super/subcritical state) and converting into sugar; and (c) a process of producing ethanol by converting a cellulose-based starting material into sugar by an enzymatic method.
JP-A-8-157644, JP-A-11-36191, and JP-A-8-260231, and WO00-53832 disclose treating cellulose with phosphoric acid and titanium to biodegrade the cellulose. In the processes described in these publications, even when cigarette filters, for example, made of cellulose acetate and the like are discarded and allowed to stay in the natural environment, the risk of environmental pollution is low, and these processes are essentially different from the process in accordance with the present invention by which useful monosaccharides are obtained by decomposition by intensive irradiation of ultraviolet rays.
Thus, the treatment of cellulose with phosphoric acid and titanium oxide imparts the cellulose with photodecomposition ability, but cellulose cannot be completely decomposed in this way under natural conditions, and it can be said that the aforementioned techniques are suitable merely as measures against littering with cigarettes and used to facilitate decomposition with enzymes or microorganisms.
A process of dissolving vegetable fibers in high-concentration phosphoric acid and bringing into contact with a hydrogen halide catalyst is disclosed, for example, in JP-A-8-299000. This process is very dangerous because a halide gas is used. Furthermore, concerns are associated with gas recovery and gas-induced corrosion.
Methods for dissolving lignocellulose that have heretofore been known are disclosed in JP-A-61-261358, JP-A-62-79230, JP-A-2-101093, JP-A-5-140322, JP-A-5-140323, JP-A-6-12277, JP-A-6-226711, and JP-A-7-118293 and in subsequently published JP-A-2000-273183, JP-A-2000-325921, JP-A-2003-342289, JP-A-2006-28040 and the like. With these methods, an organic solvent such as a phenol and an alcohol is added to lignocellulose and heating is conducted at 100° C. to 300° C. The treatment is conducted in a high-pressure pot to prevent the organic solvent from evaporating and scattering, and concerns are associated with ignition.
With respect to JP-A-10-110001, JP-A-10-251522, and JP-A-10-66594, in the process described in JP-A-10-110001, cellulase (enzyme) is used for decomposition into glucose.
In the process described in JP-A-10-251522, lignocellulose is heated and carbonized at 250° C. to 300° C., but the inflammation point of wood is usually about 270° C., the process has to be implemented in an oxygen-free atmosphere, and there is a risk of catching fire in the presence of oxygen.
JP-A-2002-85100 discloses a method for hydrolyzing cellulose with a lanthanoid source and pressurized steam at 200 to 270° C., and JP-A-2006-263527 discloses a method for hydrolyzing cellulose in a super/subcritical state.
JP-A-2005-168335 also discloses a method for converting lignocellulose into sugar by hydrothermal treatment and an enzymatic method, and JP-A-2006-2840 discloses a method by which heating is conducted at 190° C. to 300° C. in an organic solvent with a high boiling point and separation is performed by column chromatography.
JP-A-2005-40106, JP-A-2006-75007 and JP-A-2006-281037 disclose that production of glucose from a cellulose-based substance with concentrated sulfuric acid or diluted sulfuric acid causes problems with subsequent separation of sulfuric acid and corrosion of equipment.    [Patent Document 1] (1) JP-A-61-261358, (2) JP-A-62-79230, (3) JP-A-2-101093, (4) JP-A-5-140322, (5) JP-A-5-140323, (6) JP-A-6-12277, (7) JP-A-6-226711, (8) JP-A-7-118293, (9) JP-A-8-157666, (10) JP-A-8-225653, (11) JP-A-8-260231, (12) JP-A-8-299000, (13) JP-A-10-66594, (14) JP-A-10-110001, (15) JP-A-10-251522, (16) JP-A-11-36191, (17) JP-A-11-325921, (18) JP-A-2002-85100, (19) JP-A-2003-213584, (20) JP-A-2003-342289, (21) JP-A-2005-168335, (22) JP-A-2005-239979, (23) JP-A-2005-40106, (24) JP-A-2005-263527, (25) JP-A-2006-75007, (26) JP-A-2006-281037, and (27) WO00-53832.